1. Field of the Invention
The present invention generally relates to voltage generating apparatuses, and relates to a voltage generating apparatus for supplying a DC voltage to an electrophotographic image forming apparatus.
2. Description of the Related Art
An image forming apparatus using an electrophotographic process transfers a toner image carried on an intermediate transfer belt to a sheet by a secondary transfer roller. To facilitate the transfer, a transfer voltage of several kV is applied to the secondary transfer roller. In connection to this, there are cases where the toner remaining on the intermediate transfer belt adheres to the secondary transfer roller, and is further transferred from the secondary transfer roller to the back face of the sheet (back staining phenomenon). In Japanese Patent Laid-Open No. 2004-145297, application of a cleaning reverse bias before the secondary transfer and after completion of the secondary transfer in order to suppress such a phenomenon is proposed. This reverse bias causes the toner to be reverse transferred from the secondary transfer roller to the intermediate transfer belt, and the toner is collected from the intermediate transfer belt by a cleaning mechanism.
Incidentally, it is conceivable to shorten the sheet interval (the interval between the trailing end of the preceding sheet and the leading end of the subsequent sheet) in order to shorten the time required at the time of successively forming images. However, if the sheet interval time is shortened, the time during which the cleaning reverse bias is applied is also shortened, and therefore, cleaning may be insufficient. In order to switch the secondary transferring normal bias to the cleaning reverse bias, a certain amount of time is required to raise the reverse bias. For this reason, not all of the sheet interval time can be used for cleaning. Sufficient cleaning can be performed within a short sheet interval time if the raising time for the reverse bias during switching from the secondary transferring normal bias to the reverse bias is shortened. However, if the raising time for the reverse bias is to be shortened, undershoot occurs and the reverse bias cannot be easily stabilized.